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Intrinsic factors of seafood products affecting histamine formation of Morganella morganii and Proteus vulgaris |
S. H. KIM1, R. J. Price2, M. T. Morrissey1, and H. An3. (1) OSU-Seafood Lab, Oregon State University, 2001 Marine Dr., Astoria, OR 97103, (2) Dept. of Food Science and Technology, University of California, Davis, CA 95616, (3) Dept. of Nutrition and Food Science, Auburn University, 328 Spidle Hall, Auburn, AL 36849 Histamine is a chemical health hazard causing scombroid poisoning. Fish rich in free histidine are particularly susceptible to histamine formation, since they promote growth of bacteria synthesizing histidine decarboxylase. Most histamine formers are mesophilic bacteria; thus, rapid chilling of fish postharvest and storage below refrigeration temperature are commonly used in controlling histamine formation. To ensure product safety, growth of prolific histamine formers and histamine formation were monitored under controlled intrinsic conditions of seafood products. A total of 1,000 histamine formers were isolated from mackerel and albacore. The most frequently isolated prolific histamine formers, Morganella morganii and Proteus vulgaris, were inoculated at 102 cells/mL into TSBH and incubated at 25°C. The tested pHs in media ranged from 4.0 to 8.0; the salt concentrations, 1, 3, 5, and 7%; and the histidine concentrations, 1, 2, 3, 5, and 7%. Bacterial growth and histamine formation were determined by the FDA BAM and AOAC methods, respectively. M. morganii and P. vulgaris grew rapidly on the tested conditions. M. morganii produced slightly higher levels of histamine than P. vulgaris, but the two species showed similar trends in histamine production. Histamine, >2,000 ppm, was accumulated in the stationary phase of the bacterial growth. Slightly acidic pH range (pH 5.0-6.0) similar to that of fish muscle promoted histamine accumulation. Optimum salt concentration for histamine production was 3%, but the toxicological level of histamine (>500 ppm) was accumulated even at 7% salt. The histamine levels in the media increased, as the histidine concentrations increased. Bacterial growth and histamine formation were inhibited only at pH 4, the condition rarely found with fish products. M. morganii and P. vulgaris produced high levels of histamine at broad ranges of intrinsic factors tested, indicating the possibility of histamine formation in various fish species and seafood products. Their proliferation should be tightly monitored to prevent histamine formation during handling, processing, and distribution of seafood products.
Session 42, Seafood Technology: Safety, Processing
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